With Spring finally here, many more people are out biking. Some wear helmets, some don't. Helmet-wearing is generally taken to be beneficial, especially when looking at the incidence of serious head injuries. See, for instance, the 2011 study "The Impact of Compulsory Cycle Helmet Legislation on Cyclist Head Iinjuries in New South Wales, Australia ," by Scott R. Walker et al. (Accident Analysis and Prevention, 43(6):2064-2071 (Nov. 2011). The authors found that "[h]ead injury rates decreased significantly more than limb injury rates at the time of legislation among cyclists but not among pedestrians. This additional benefit was attributed to compulsory helmet legislation. Despite numerous data limitations, we identified evidence of a positive effect of compulsory cycle helmet legislation on cyclist head injuries at a population level such that repealing the law cannot be justified."